In semiconductor devices such as power transistors breakdown voltage and on-state resistance depend on parameters such as doping and thickness of a drift zone. Whereas a high doping density and a short extension of a drift zone may lead to a low on-state resistance and a low device breakdown voltage, lower doping densities and longer extensions of the drift zone may lead to a higher on-state resistance and a higher device breakdown voltage. In order to improve both, lowering the on-state resistance and increasing the voltage blocking capability, a decoupling between these two measures is desirable. One configuration of a vertical MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a TEDFET (Trench Extended Drain Field Effect Transistor) which allows for an improved decoupling of voltage blocking capability and on-state resistance compared to conventional MOSFETs by controlling the conductivity in the drift zone by drift control zones. Manufacture of TEDFETs may include processes having a considerable impact on costs and device reliability.
With regard to a semiconductor device including drift zones and drift control zones, a need exists for an improved device reliability.
For these and other reasons, there is a need for the present invention.